JP2006007860A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform auxiliary steering in correspondence with the actual stopping and traveling state when abnormality of a sensor signal of a vehicle speed sensor is recognized. <P>SOLUTION: This electric power steering device for performing auxiliary steering by driving an electric motor 5 in accordance with operation of a steering member 1 is provided with a torque sensor 3 for detecting steering torque, the vehicle speed sensor 15 for detecting a vehicle speed, a control means 181a for driving and controlling the electric motor 5 based on the sensor signal of the sensors 3 and 15, a vibration sensor 14 for detecting vibration of the vehicle, and a storage means 183 for storing a control map mb determining driving quantity of the electric motor 5 for each of the traveling states including the stopping state. When abnormality of the sensor signal of the vehicle speed sensor 15 is recognized, the control means 181a refers to the control map mb by the traveling state in correspondence with the sensor signal of the vibration sensor 14 in stead of the vehicle speed sensor 15, and the driving quantity of the electric motor 5 is determined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that assists a driver's steering force by driving an electric motor in accordance with an operation of a steering member such as a steering wheel.

  Generally, an electric power steering apparatus is based on various sensors (a torque sensor for detecting a steering torque applied to a steering member, a vehicle speed sensor for detecting a vehicle speed, etc.), an electric motor for assisting steering, and sensor signals from the various sensors. An electronic control unit (ECU) that calculates a motor current command value to the motor drive circuit and controls the drive of the electric motor, and drives the electric motor according to the control command of the ECU to steer the steering assist torque. In addition to the mechanism, the driver's steering force is reduced (see Patent Document 1).

  In the conventional electric power steering control, the safety against abnormalities such as failure and disconnection of various sensors is maintained at a certain level by fail-safe operation corresponding to these abnormalities.

  By the way, in general, the electric power steering control is a vehicle speed sensitive type. When the vehicle speed is low, the steering assist torque is relatively large so that the steering operation can be performed lightly, and at a high vehicle speed, the steering operation is heavy. Thus, the steering assist torque is further reduced, and the steering assist is performed with an additional torque corresponding to the vehicle speed. When the sensor signal of the vehicle speed sensor is abnormal, the steering assist is continued by fixing the relationship between the steering torque and the steering assist torque to a certain constant without stopping the steering assist as a corresponding fail-safe operation. It is possible.

However, in this fail-safe operation, from the viewpoint of improving safety, the above constant is a value that generates a relatively small steering assist torque (if the steering assist torque is large, the steering wheel is turned off during high-speed traveling). Too much to compromise safety). Therefore, the steering becomes heavy when traveling at a low vehicle speed, and the steering feeling is extremely poor.
JP-A-6-56045

  Therefore, the problem to be solved by the present invention is that, even if the sensor signal of the vehicle speed sensor is abnormal due to failure of the vehicle speed sensor itself, the steering assistance by the electric motor is performed according to the actual running state. Another object is to provide an electric power steering device that can maintain a good steering feeling.

  An electric power steering apparatus according to the present invention is an electric power steering apparatus that assists steering by driving an electric motor in accordance with an operation of a steering member, and detects a steering speed applied to the steering member and a vehicle speed. Vehicle speed sensor, control means for driving and controlling the electric motor based on both sensor signals of the torque sensor and the vehicle speed sensor, a vibration sensor for detecting the vibration of the vehicle, and a plurality of driving states including a stop state as parameters. Storage means for storing a control map for determining the drive amount of the electric motor each time, and the control means corresponds to the sensor signal of the vibration sensor instead of the vehicle speed sensor when the sensor signal of the vehicle speed sensor is abnormal. The drive amount of the electric motor is determined by referring to the control map according to the running state.

  In the above configuration, the sensor signal abnormality of the vehicle speed sensor includes not only a failure of the vehicle speed sensor itself, but also a connection abnormality such as disconnection of the power line or signal line of the vehicle speed sensor, and an abnormality of the sensor signal due to other factors.

  Moreover, in the said structure, a vehicle speed sensor is not limited to what was provided exclusively in order to detect a vehicle speed, The vehicle speed sensor contained in the other electronic control unit (ECU) with which the said vehicle is equipped is included.

  Further, in the above configuration, the vibration sensor is not limited to a dedicated sensor for detecting the vibration of the vehicle, but is a G pickup sensor included in another electronic control unit (ECU) installed in the vehicle. In addition, a vehicle height sensor is also used as a vibration sensor that detects vehicle vibration.

  The present invention pays attention to the fact that the frequency of the vibration of the vehicle corresponds to the stop / running state of the vehicle. According to the above configuration, when the sensor signal of the vehicle speed sensor is abnormal, the vehicle speed sensor Instead, using the driving state corresponding to the sensor signal of the vibration sensor as a parameter, the driving amount of the electric motor is determined according to the control map of the storage means, and the electric motor is driven and controlled. Therefore, accurate information on the actual vehicle speed is input. Even without it, it is possible to assist steering according to the state of stopping / running. For example, it can be set so that the steering operation is light at low speeds and heavy at high speeds, and the steering feeling is maintained at a certain level. It can be secured. Therefore, for example, when an abnormality of the vehicle speed sensor is found and the vehicle is moved to a dealer or a repair shop at a low vehicle speed, the steering operation can be lightened to reduce the steering effort.

  According to the present invention, even when the sensor signal of the vehicle speed sensor is abnormal, it is possible to perform the electric power steering control with excellent steering feeling by making the steering assist compatible with the actual traveling state.

  Hereinafter, an electric power steering apparatus according to the best mode of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing the electric power steering apparatus of the present embodiment together with a vehicle configuration related thereto.

  Referring to FIG. 1, the electric power steering apparatus according to the present embodiment includes a steering shaft 2 having one end fixed to a steering member 1 such as a steering wheel (handle), and a driver's steering torque applied to the steering shaft 2. Steering assistance for reducing the driver's load due to the operation (steering operation) of the steering member 1 and the torque mechanism 3 to be detected, the steering mechanism 4 composed of a rack and pinion mechanism or the like connected to the other end of the steering shaft 2 The electric motor 5 that generates force, the speed reduction mechanism 6 that transmits the steering assist torque generated by the electric motor 5 to the steering shaft 2, and the power supply from the in-vehicle battery 7 via the ignition switch 8, An electronic power steering electronic control unit (EPS ECU) 10 that controls driving is provided.

  The steering shaft 2 is divided into at least a portion on the steering member 1 side and a portion on the steering mechanism 4 side, and both portions are connected by a torsion bar 9, and the torque sensor 3 is disposed on the outer periphery of the torsion bar 9. Has been. An output side of the steering mechanism 4 is connected to a steering wheel 12 via a connecting member 11 including a tie rod and a knuckle arm.

  The EPS ECU 10 has a CAN (controller area network) controller 101 inside, is connected to the CAN bus 13 via the CAN controller 101, and is connected to the CAN bus 13. Together with the ECUs 20, 30, 40, 50, an in-vehicle CAN communication system is configured. The CAN controller 101 has functions of data reception processing, response data creation processing, and data transmission processing, and CAN communication with CAN controllers 201, 301, 401, and 501 included in other ECUs 20, 30, 40, and 50. And the sensor signal of the sensor contained in the said other ECU20-50 can be received, or the sensor signal of the sensor contained in the own ECU10 can be transmitted to other ECU20-50. The CAN bus 13 includes two communication lines and can perform differential serial communication.

  In general, the CAN communication system is known as a network system for connecting a plurality of devices such as in-vehicle devices and home appliances, and has a maximum transmission rate of 1 Мbps, compared with a communication method used conventionally. It has the feature of being very fast. Moreover, since it is serial communication which replaces a digital signal with the differential voltage between two wires, it also has the feature of being excellent in noise resistance.

  In this CAN communication system, the ECUs 10 to 50 as nodes can communicate data such as sensor signals as packets on the CAN bus 13 as long as the CAN bus 13 is free. When the CAN bus 13 is occupied by packets from other ECUs 10 to 50, the packets to be sent stand by at the CAN controllers 101, 201, 301, 401, and 501 provided in the ECUs 10 to 50. Further, the plurality of ECUs 10 to 50 can simultaneously receive packets on the CAN bus 13.

  Packets flowing on the CAN bus 13 are transmitted by varying the identification number of the ECU 10 to 50 or the ID field for storing the data type, the control field for storing the data length of the data field, and 0 to 8 bytes. A data field for storing power data and a CRC field for storing data for performing cyclic code redundancy check. Each of the ECUs 10 to 50 has a transmission speed of 500 kbps, for example, and can transmit 1 frame data of about 120 bits in about 250 μs when the data length of the data field is 8 bytes. .

  In the present embodiment, as other ECUs that constitute an in-vehicle CAN communication system together with the EPS ECU 10, a VSC (registered trademark) ECU 20 that stabilizes the turning behavior of the vehicle, and the acceleration and straightness of the vehicle. There is a TRC (registered trademark) ECU 30 for ensuring turning stability, an ABS (anti-lock brake system) ECU 40 for preventing wheel locking, and other ECUs 50.

  Each of the ECUs 10 to 50 including the EPS ECU 10 includes a single or a plurality of sensors in addition to the CAN controllers 101 to 501. For example, the VSC ECU 20 is provided with a G pickup sensor (gravity acceleration sensor) 14 for detecting the gravitational acceleration applied to the vehicle, and the ABS ECU 40 includes a vehicle speed sensor 15 for detecting the rotational speed of each wheel. It is. The other ECU 50 includes a vehicle height sensor 16. In the present embodiment, the EPS ECU 10 takes in the sensor signal of the vehicle speed sensor 15 and the sensor signal of the G pickup sensor 14 as a sensor for detecting the vibration of the vehicle through the CAN controller 101 and the CAN bus 13. ing.

  In a vehicle equipped with the electric power steering device, when the driver operates the steering member 1, the steering torque due to the operation is detected by the torque sensor 3. The EPS ECU 10 controls the driving of the electric motor 5 based on the steering torque detected by the torque sensor 3 and the vehicle speed information of the vehicle speed sensor 15 captured by CAN communication. As a result, the electric motor 5 generates steering assist torque, and this steering assist torque is applied to the steering shaft 2 via the speed reduction mechanism 6, thereby reducing the burden on the driver who performs the steering operation. That is, the sum of the steering torque applied by the operation of the steering member 1 and the steering assist torque generated by the electric motor 5 is given as an output torque to the steering mechanism 4 via the steering shaft 2. As a result, the input shaft of the steering mechanism 4 rotates, and the rotation is converted by the steering mechanism 4 into a reciprocating motion of the rack shaft that is the output shaft, and the direction of the wheel 12 changes according to the reciprocating motion of the rack shaft.

  Next, the configuration of the EPS ECU 10 will be described with reference to FIGS. 2 is a block circuit diagram inside the EPS ECU 10, FIG. 3 is a functional block diagram showing the operation of the microcomputer of the EPS ECU 10, and FIG. 4 is a diagram showing a control map stored in the map memory of the EPS ECU 10. is there.

  Referring to FIG. 2, in addition to the above-mentioned CAN controller 101, the EPS ECU 10 includes an input interface 17 for processing the sensor signal of the torque sensor 3, a microcomputer 18 that controls the center of electric power steering control, and a microcomputer. A motor drive circuit 19 that drives the electric motor 5 in response to a control signal from 18 and a power supply circuit 21 that supplies power to each circuit other than the motor drive circuit 19 are provided.

  Around the motor drive circuit 19, there are a fail safe relay 22 for turning on and off the current to the motor drive circuit 19, a drive circuit 23 for the fail safe relay 22, and a terminal voltage on the output side of the fail safe relay 22. A fail safe relay terminal voltage monitoring circuit 24 that monitors the motor current, a motor relay 25 that turns on and off the motor current on the output side of the motor drive circuit 19, a drive circuit 26 of the motor relay 25, and an output side of the motor relay 25 And a motor relay terminal voltage monitoring circuit 27 for monitoring the terminal voltage.

  The microcomputer 18 includes a CPU 181, a program memory 182, a map memory 183, and a buffer memory 184.

  Among these, the function of the CPU 181 will be described with reference to FIG. 3. In this embodiment, the CPU 181 is based on sensor signals from the torque sensor 3 and the like, as will be described in detail later with reference to a flowchart. In addition to functioning as a control means 181a for determining the driving amount of the vehicle, the sensor abnormality detection means 181b for detecting an abnormality in the sensor signal of the vehicle speed sensor 15, the vehicle is stopped, driven at low speed, and driven at high speed based on the sensor signal of the G pickup sensor The control means 181a functions as vehicle state information obtained from the vehicle speed sensor 15 when the sensor signal of the vehicle speed sensor 15 is normal. The driving amount of the electric motor 5 is determined based on the steering torque information obtained from the torque sensor 3. When the abnormality of the sensor signal 5 is detected, the driving of the electric motor 5 is driven based on the traveling state determined by the traveling state determination unit 181c based on the sensor signal of the G pickup sensor 14 and the sensor signal of the torque sensor 3. The amount is to be determined.

  The program memory 182 stores a basic program for executing the operation of the CPU 181 and a program necessary for executing drive control of the electric motor 5 of this embodiment, and the map memory 183 stores the program of the electric motor 5 of this embodiment. A control map (first control map ma and second control map mb) necessary for execution of drive control is stored. The buffer memory 184 is used for temporary storage of data when the CPU 181 performs work.

  The first and second control maps stored in the map memory 183 will be described with reference to FIG. A first control map ma shown in FIG. 4A is a control map that should be referred to by the CPU 181 when the sensor signal of the vehicle speed sensor 15 is normal, and shows the relationship between the steering torque and the drive amount of the electric motor 5. . In the control map ma, the horizontal axis represents the steering torque (Nm), the vertical axis represents the driving amount of the electric motor 5 (target motor current value: A), and the vehicle speed (km / h) is a parameter, and the traveling speed is The driving amount of the electric motor 5 with respect to the steering torque can be determined for each vehicle speed of 0 km / h, 10 km / h, 60 km / h, 100 km / h, and 180 km / h.

  The second control map mb shown in FIG. 4B is a control map that should be referred to by the CPU 181 when the sensor signal of the vehicle speed sensor 15 is abnormal. Like the first control map ma, the steering torque (Nm) is plotted on the horizontal axis. The driving amount of the electric motor 5 (target motor current value: A) is taken on the vertical axis, and the rough running state, that is, the stopped state and the two high and low running states are used as parameters, and the stopped state, the low speed running state, and the high speed The driving amount of the electric motor 5 with respect to the steering torque can be determined for each traveling state of the traveling state.

  Next, the operation when the microcomputer 18 of the EPS ECU 10 performs steering assist control will be described with reference to the flowchart of FIG. The microcomputer 18 periodically executes the steps shown in the figure every predetermined time, for example, every 10 ms, by a predetermined timer interruption or the like.

  In step S1, it is determined whether or not each sensor signal is normal for each sensor (for example, torque sensor 3 and vehicle speed sensor 15) that has always taken in the sensor signal. The vehicle speed sensor 15 is performed, for example, by determining whether or not a predetermined reference value that can change in a certain time (for 10 ms) is exceeded from the difference between the previous detected vehicle speed and the current detected vehicle speed. If there is no abnormality in the sensor signal for any sensor in step S1 (YES in S1), the process proceeds to step S2, and the steering torque information obtained from the torque sensor 3 and the vehicle speed information obtained from the vehicle speed sensor 15 are used. Referring to the first control map ma, the driving amount of the electric motor 5 is determined, and the electric motor 5 is driven to perform steering assistance.

  If it is determined in step S1 that one of the sensor signals is not normal (abnormal) (NO in S1), the process proceeds to step S3, and whether or not the abnormality of the sensor signal is related to the vehicle speed sensor 15. Determine whether. If the abnormality of the sensor signal is related to a sensor other than the vehicle speed sensor 15 (NO in S3), a predetermined fail safe routine rs corresponding to the abnormality of the sensor signal other than the vehicle speed sensor 15 is entered, and a predetermined fail safe operation is performed. For example, operations such as displaying the contents of abnormality and stopping the steering assist by the electric motor 5 are performed.

  If it is determined in step S3 that an abnormality has occurred in the sensor signal of the vehicle speed sensor 15 (YES in S3), the process proceeds to step S4.

  In step S4, the microcomputer 18 requests the ECU (VSC ECU) 20 including the G pickup sensor 14 to transmit a sensor signal of the G pickup sensor 14 via the CAN controller 101 of the EPS ECU 10. The ECU 20 including the G pickup sensor 14 transmits the sensor signal of the G pickup sensor 14 in response to the request for the sensor signal from the EPS ECU 10. Thereby, the microcomputer 18 of the EPS ECU 10 takes in the sensor signal of the G pickup sensor 14 as a signal indicating the vibration of the vehicle.

  In the next step S <b> 5, the microcomputer 18 determines the stop / running state of the vehicle based on the vehicle vibration data received from the G pickup sensor 14. That is, when there is no vibration of the vehicle, it is determined that the vehicle is in a stopped state. When the vibration frequency of the vehicle is low, it is determined that the vehicle is in a low speed traveling state. When the vibration frequency of the vehicle is high, the vehicle is in a high speed traveling state. It progresses to step S6.

  In step S6, the driving amount of the electric motor 5 is obtained by referring to the second control map mb of the map memory 183 according to the stop / running state of the vehicle determined based on the vibration data instead of the vehicle speed sensor 15. That is, when there is no vibration of the vehicle, the parameter is set to the stop state, and the driving amount of the electric motor 5 is obtained by referring to the second control map mb with this parameter and the steering torque data obtained from the torque sensor 3. The electric motor 5 is driven and controlled in accordance with the obtained driving amount of the electric motor 5.

  On the other hand, when the vibration frequency of the vehicle is low, the parameter is set to a low-speed running state, the second control map mb is referred to by this parameter and the steering torque data obtained from the torque sensor 3, and the electric motor corresponding to them is referred to. The driving amount of the motor 5 is obtained. When the vibration frequency of the vehicle is high, the parameter is set to a high-speed running state, the second control map mb is referred to with this parameter and the steering torque data obtained from the torque sensor 3, and the electric motor 5 corresponding to them is referred to. Find the drive amount.

  Thus, even when the sensor signal of the vehicle speed sensor 15 is abnormal, it is possible to perform the steering assist corresponding to the traveling state determined from the vibration state of the vehicle.

  FIG. 6 is a flowchart showing another operation of the microcomputer 18. As shown in FIG. 2, the EPS ECU 10 is provided with relays such as a fail safe relay 22 and a motor relay 25. The relays 22 and 25 may be fixed while the contacts are welded or opened by biting foreign matter such as metal powder between the contacts.

  In the routine shown in this flowchart, when the ignition switch 8 is turned on, the fail safe relay 22 and the motor relay 25 are turned on / off via the relay drive circuits 23 and 26 in step T1, respectively. At T2, the output side terminal voltages of the relays 22 and 25 are monitored via the terminal voltage monitoring circuits 24 and 27, respectively. If the relays 22 and 25 are not broken and are normal, terminal voltages corresponding to ON / OFF of the relay drive circuits 23 and 26 should appear on the output side of the relays 22 and 25.

  In the next step T3, the number of attempts to turn on / off the relays 22 and 25 is counted. In step T4, whether or not the operations of the relays 22 and 25 are normal, that is, the relays 22 and 25 are counted. It is determined whether or not a terminal voltage corresponding to ON / OFF of the relay drive circuits 23 and 26 appears on the output side of the relay. If the operation of each relay 22 and 25 is normal (YES at T4), Since there is no problem in each of the relays 22 and 25, a normal electric power steering (EPS) control operation is started.

  If the operation of one of the relays 22 and 25 is not normal in step T4 (NO in T4), the process proceeds to step T5, and the number of trials of the on / off operation is a predetermined number (3 or 5 times). If the predetermined number of trials has not been reached (NO in T5), the process returns to step T1 and repeats the trial of ON / OFF operation of the relays 22 and 25. . If each of the relays 22 and 25 does not operate normally even if the on / off operation is attempted again, the on / off operation is repeated until the predetermined number of times is reached.

  In many actual relays, even if the first on / off operation is not performed normally, there are many relays that operate normally after repeating the trial twice or three times. This is considered that the operation abnormality due to the biting of the foreign matter is solved by the forced operation.

  If the relays 22 and 25 operate normally before the number of trials reaches the predetermined number, normal EPS control operation starts from step T4. If any of the relays 22 (25) does not operate normally after a predetermined number of on / off operation attempts (YES at T5), the relay 22 (25) is in an abnormal state with no expectation of recovery. Therefore, in this case, a fail-safe routine rr corresponding to the abnormality of the relay is entered, and this is displayed on the indicator of the driver's seat, and the steering assist by the electric motor 5 is stopped. Take action.

The block diagram which shows the electric power steering device which concerns on the best form of this invention with the vehicle structure relevant to it The block circuit diagram which shows the internal structure of ECU for EPS of the electric power steering apparatus of FIG. Functional block diagram showing the operation of the microcomputer of the EPS ECU of FIG. The figure which shows the control map which the map memory of the microcomputer of EPS ECU of FIG. 2 memorize | stores Flowchart for explaining the operation of the microcomputer of the EPS ECU in FIG. Flowchart for explaining another operation of the microcomputer of the EPS ECU in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering member 2 Steering shaft 3 Torque sensor 4 Steering mechanism 5 Electric motor 10 Electronic power steering electronic control unit (ECU for EPS)
101 CAN controller 13 CAN bus 14 G pickup sensor (vibration sensor)
15 Vehicle speed sensor 18 Microcomputer 181 CPU
181a Control means 181b Sensor abnormality detection means 181c Traveling state determination means 183 Map memory (storage means)
20, 30, 40, 50 Other ECUs

Claims (1)

An electric power steering device that assists steering by driving an electric motor according to an operation of a steering member,
A torque sensor for detecting a steering torque applied to the steering member;
A vehicle speed sensor for detecting the vehicle speed;
Control means for driving and controlling the electric motor based on both sensor signals of the torque sensor and the vehicle speed sensor;
A vibration sensor for detecting the vibration of the vehicle;
Storage means for storing a control map for determining the driving amount of the electric motor for each parameter using a plurality of driving states including a stop state as parameters,
The control means determines the drive amount of the electric motor with reference to the control map according to the running state corresponding to the sensor signal of the vibration sensor instead of the vehicle speed sensor when the sensor signal of the vehicle speed sensor is abnormal.
An electric power steering device.

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